<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>初识JavaScript</title>
</head>
<body>
 <input name="btn" type="button" value="弹出消息框" onclick="javascript:
        alert('您好 JavaScript ');"/>
<script type="text/javascript" src="js/index.js"></script>
</body>
</html>